Paper packaging materials for liquid food having excellent light barrier ability and a method of manufacturing are disclosed.
A method of manufacturing paper packaging materials for liquid food provides for promptly finding damage of the inside layers of a paper layer as a core layer having excellent light barrier ability.
Paper containers comprised of a laminated material of paper and thermoplastic resin are widespread as a container of liquid food, such as juice, coffee, milk, and liquor.
As for the paper container, the outermost layer (layer contacting outside air) and an innermost layer (layer contacting liquid food) usually consist of a thermoplastic resin layer. However, the paper container is a poor light barrier. Contents of milk and the like are deteriorated due to visible light.
For contents that are sensitive to ultraviolet light, aroma is decreased by transmitted ultraviolet light.
In order to make the paper container have light barrier capabilities, laminating aluminum foil or surface-coating carbon black are not practical in view of point of cast-problem and environment.
While filling up liquid food in a paper container and manufacturing packaging materials for the paper container, the internal layer of the packaging materials may have small defects like pinholes. With pinholes, liquid food contents leak out and reach the paper layer. The contents cannot be protected.
Conventionally, a method of using coloring ink forcefully is employed to inspect damage of the internal layer. However, the test method is complicated and requires much time.